Light emitting diodes (“LEDs”) are ubiquitous in electronics. They are used in digital displays, lighting systems, computers and televisions, cellular telephones and a variety of other devices. Developments in LED technology have led to methods and systems for the generation of white light using one or more LEDs. Developments in LED technology have led to LEDs that generate more photons and thus more light than previously. The culmination of these two technological developments is that LEDs are being used to supplement or replace many conventional lighting sources, e.g. incandescent, fluorescent or halogen bulbs, much as the transistor replaced the vacuum tube in computers.
Current industry practice for construction of LEDs is to use a substrate (typically either single-crystal Sapphire or Silicon Carbide), onto which is deposited layers of materials such as GaN or InGaN. One or more layers (e.g. GaN or InGaN) may allow photon generation and current conduction. Typically, a first layer of Gallium Nitride (GaN) is applied to the surface of the substrate to form a transition region from the crystal structure of the substrate to the crystal structure of doped layers allowing for photon generation or current conduction. This is typically followed by an N-doped layer of GaN. The next layer can be an InGaN, AlGaN, AlInGaN or other compound semiconductor material layer that generates photons and that is doped with the needed materials to produce the desired wavelength of light. The next layer is typically a P doped layer of GaN. This structure is further modified by etching and deposition to create metallic sites for electrical connections to the device.
In recent years, LED manufacturers have produced thin-film LEDs. In thin-film LEDs, the substrate is removed and the GaN layer thinned to approximately 2-3 μm. In some cases a replacement substrate is applied to the thinned GaN. Light is generated in the GaN layer and must escape to the surrounding medium. However, the light can become trapped in the GaN layer due to internal reflection in the GaN and only the light that is within the escape cone actually makes it into air or the substrate. The rest of the photons are trapped within the material and eventually get absorbed as heat. The current solution to alleviate this problem is to roughen the GaN to disrupt the waveguide effect.